Could a Gravity Trick Speed Us to Mars?

Putting a human on Mars might be easier than anyone thought. A flight to the Red Planet currently takes at least six months, which is why we send robots—the trip is boring, fuel costs are astronomical, and cosmic radiation is nobody's friend. But NASA engineer Robert Adams has a solution: the two-burn maneuver, an all-but-forgotten secret of orbital mechanics that could cut travel time in half.

Dreamed up in 1929 by Hermann Oberth, one of the fathers of rocket science, the technique relies on the simple fact that faster-moving objects have more energy than slower ones. So, let's say you're in a spaceship at a fueling station in Earth orbit, near the moon: First you thrust back toward the planet (burn number one), where the force of gravity accelerates the craft. Then you point yourself in the right direction and punch the rockets again (burn number two). The result? "More bang for the buck from my propellant," Adams says.

Oberth came up with the maneuver when space travel was still just writing on a chalkboard. Thanks to Adams, NASA considered trying it on a planned mission to the moon. But he says the savings don't really kick in until you think bigger. Use the extra fuel to blast people to Mars faster, or save money by building a smaller ship. After that? We hear the Jovian moons are lovely in springtime.